RosettaCodeData/Task/Longest-common-substring/Yabasic/longest-common-substring.basic

sub LCS$(a$, b$)
    if len(a$) = 0 or len(b$) = 0  return
	while len(b$)
		for j = len(b$) to 1 step -1
			if instr(a$, left$(b$, j))  return left$(b$, j)
		next j
		b$ = mid$(b$, 2)
	wend
end sub

print LCS$("thisisatest", "testing123testing")
end